Low thermal expansion ceramic material



United States Patent ()fice f iiffii 3 549 394 coefficient of expansion of the solid solutions of this LOW THERMAL EXPANSION mvemlon- CERAMIC AL LINEAR THERMAL EXPANSION DATA FOR PHOSPHORUS Anthony J. Perrotta, Nanuet, N.Y. LITHIUM ALUMINOSILICATE BODIES (950 Harvard Road, Monroeville, Pa. 15146) No Drawing. Filed Dec. 18, 1967, Ser. No. 691,148

Int. Cl. C04b 33/00 20 so 40 50 65 US. Cl. 106-39 3 Cl 100 -0,05 --0.04 +0.03 -0.02 -0.01 +0.01 +0.02 -0.15 -0.08 -0.03 +0.03 +0.00

ABSTRACT OF THE DISCLOSURE 0 .40 0'.27 -01 16 +005 +0111 A single phase solid solution of beta-eucryptite and A1PO4 having the formula Although many prior art and industrial ceramics are U AIP Si 0 known which have extremely low coeflicient of thermal X 4 expansion, insofar as the present inventor is aware all wherein x is between 0.05 and 0.65. such materials consists of two phases, while the present material consists of a single phase solid solution and, therefore, possesses numerous advantages over such prior This invention relates to a ceramic material having a art and commercial compositions, e.g., it exhibits envery low coefiicient of thermal expansion and to the 20 hanced thermal shock resistance, variable thermal expreparation of said material. More specifically, it relates pansion properties, inexpensive production due to availto materials having chemical constituents represented by ability and cost of materials and facility of preparation. the general formula It is believed that the intrusion of a pentavalent ion into the crystal lattice occurs only at the tetrahedral sites L11XA1PXSl1XO4 and that each atom of phosphorus replaces both a lithium atom and a silicon atom in the crystal lattice.

Glasses and glass ceramics can be formed in this phosphorus bearing compositional range. New beta-quartz glass ceramics may be formed with nucleating agents such as zirconia or titania by recrystallization of the glasses. Cation exchange or substitution on tetrahedral sites (phosphorus for silicon) besides the commonly used, for example 2Li+ for Mg can be done giving surfaces under a state of compression via the differences in the expansion coefficients which should give increased fiexural strengths. These beta-quartz ceramics are more thermally stable than the meta-stable beta-quartz ceramics existing in the high silica region.

With amounts of AlPO above it is necessary to heat to temperatures above 1050 C. in order to obtain a single phase solid solution. For example, for 65% MP0; temperatures above about 1200 C. are required.

Having now described the invention, it is not intended that it be limited except as may be required by the appended claims.

I claim:

1. A single phase solid solution of beta-eucryptite and MP0; having the formula wherein x lies between 0.05 and 0.65.

2. A solid solution of claim 1 produced by mixing and heating a mixture consisting of AlPO and LiAlSiO 3. A ceramic with a substantially zero coefficient of thermal expansion and having the formula of claim 1.

wherein x lies between about 0.05 and 0.65, which material is a true solid solution between LiAlSiO (betaeucryptite) and AIPO the beta-eucryptite having a betaquartz structure and the MP0,; having a cristobalite-, tridymiteor quartz-structure depending on the preparation temperature.

By varying the value of x in the above formula, it is possible to produce a ceramic material in which the coefiicient of thermal expansion may be controlled so that it is either a very small positive value or a negative value or zero, over wide ranges of temperature.

A preferred method for preparing the ceramic solid solution materials of this invention comprises mixing MP0; and LiAlSiO, in suitable proportions and then 40 heating the mixture in order to produce the desired solid solution.

In preparing the beta-eucryptite (LiAlSiO properly proportioned mixtures of reagent grade Al(OH) SiO and Li CO can be heated to temperatures sufficient to 45 drive ofi H 0 and CO and to effect combination of the oxides to produce the beta-eucryptite. Equimolar mixtures of Al(OH) and (NH HPO can be heated in the same manner to produce AlPO After a mixture of LiAlSiO (beta-eucryptite) and cristobalite structure AlPO; is formed, the mixture is pelletized and then heated for 16 hours at a temperature of 1050 C., or higher, the heating being in air. Then the product is air quenched, i.e., permitted to cool in air.

Another more economical method is by heating the natural mineral alpha-eucryptite (LiAlSiO to 900 C.-

1350 C. which will result in the conversion of the alpha- R f eucryptite to beta-eucryptite. The beta-eucryptite ma be e erences Clted mixed in the correct proportions with the natural phos- Perotta, L! and salvage, l yp Cry Phate mineral b fljnit M then heated to the talline Solutions Involving P, in J. Amer. Cer. Soc., 50 quired temperature to form the beta-eucryptite solid February 1967, P- solutions.

Depending on the relative proportions of the two pre- TOBIAS LEVOW Pnmary Examiner formed starting materials, the coeflicient of expansion of WALTER R, SATTERFI Assistant Examiner the resulting solid solution is either zero, or a small positive value or a negative value. US. Cl. X.R.

In the following table there are presented values of the -33 

